lavd/v4l2: correctly handle error conditions in mmap_read_frame()

In particular:

1) save errno before it (possibly) gets overwritten by other calls
2) do not forget to enqueue the buffer again in case of error

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
lavd/v4l2: simplify code

struct buff_data contains a pointer to struct video_data, so passing the
file descriptor again is redundant.

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
dsputil: make square put/avg_pixels functions local to h264qpel.

Put a copy of the 8bit functions only in dsputil, where they are used
for some other things (e.g. mpeg4qpel, mspel, cavsqpel). We could perhaps
also try to share specifically the 8bit functions from h264qpel between
it and the others, but that will be slightly more complicated. H264qpel
already had these functions, so we can simply remove the duplicates.

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
x86/qpel: move fullpel and l2 functions to separate file.

This way, they can be shared between mpeg4qpel and h264qpel without
requiring either one to be compiled unconditionally.

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
Revert "build: disable iconv by default."

This reverts commit 9ad3cd5b5f848eb3cd033be515d34296f099148b.

The misdetection on OS X should be fixed, we will only get
problem reports if auto-detection is enabled.